Dan has it right. You need to know what you want before you go any further. Do you already have a barrel? If its a .40 cal that is only 3/4" across the flats you want a late style gun. TOW #BP-PW-12-B 1 1/4" WIDE, 4 1/8" TALL, 1 7/8" RETURN. If you are talking about 7/8" at the flats you will be able to go a little wider at the but WHICH A TOW, #BP- MA-56-B at 1.5"WIDE, 4 1/4" TALL, 1 15/16" RETURN. If the .40 is a C wt barrel then You will want to build a Dickert from his early period and will need the Track of the Wolf # BP-LANC-2-B INVESTMENT CAST BRASS 1 7/8" WIDE, 5" TALL, 2 1/16" RETURN..